Investigation of n-ZnO/p-porous GaAs/p⁺⁺-GaAs heterostructure for photodetection applications

In this work, we have investigated n-ZnO/p-porous GaAs/p⁺⁺-GaAs heterostructure for low-cost photodetector applications. Solution-based deposition process was used to synthesize ZnO thin film on porous GaAs layer formed by anodic etching. Energy dispersive x-ray spectroscopy (EDX) was used for chemical characterization and revealed that the deposited ZnO film was oxygen rich. Scanning electron microscopy (SEM) analysis demonstrated a porous surface morphology of the ZnO film and the infiltration of a part of the deposited film inside the porous GaAs matrix. The transport mechanisms of the n-ZnO/p-porous_GaAs/p⁺⁺-GaAs heterostructure were investigated via current–voltage (I–V) measurements in the dark at room temperature. I–V characteristic showed rectification behavior, and the maximum value of the rectification ratio is 53 at ± 1.78 V. A series resistance R_s = 15 Ω and an ideality factor, n = 8, were obtained by using the Cheung function. The Forward I–V curve in Log–Log scales follows a power law dependence characteristic of trap-assisted space charge limited conduction. In the reverse bias voltages, we found that the thermionic emission theory in the presence of an interface layer reproduces the current–voltage characteristic. A potential barrier height of \({\varphi }_{B}\) ${\phi }_B$ = 580 meV and an ideality factor n = 1.06 were obtained. For more investigations, we carried out impedance spectroscopy measurements. From the Cole–Cole impedance curves of the reverse-biased device, we demonstrated the formation of two depletion regions operating in opposite directions to the applied voltage. Conductance-frequency (G-f) experimental results agree with Jonsher’s law, proving that charge transport processes across device interfaces occur by jumping between localized states. The analysis of I–V characteristic under illumination demonstrates that the n-ZnO/p-porous GaAs/p⁺⁺-GaAs device can be used for photodetection applications. The measured photocurrent reaches a value of 39 mA for an applied voltage of 1.48 V. The photocurrent spectrum showed a signal without applied voltage and confirmed the presence of an internal electric field that self-polarizes the device.